1. Field of Invention
This invention relates to target detection and missile guidance. Specifically, the present invention relates to systems and methods for locating a target, such as an unmanned vehicle, and guiding a missile or other controllable device based on the target position.
2. Description of the Related Art
Target tracking and missile guidance systems are employed in various demanding applications including infrared, radar, sonar, and laser target detection and tracking systems employed to detect and shoot down moving targets, such as miniature Unmanned Aerial Vehicles (UAV's) and anti-aircraft batteries.
Time-of-arrival techniques are often employed to locate a radiating target, such as a Surface-to-Air Missile (SAM) battery. For example, three or more aircraft may time the arrival of electromagnetic energy emanating from the SAM battery. By measuring signal arrival time from the battery to the three or more aircraft, the location of the battery is determined. Clocks on the aircraft are synchronized via Global Positioning System (GPS) satellite clocks to enhance distance computation accuracy. Subsequently, a missile equipped with GPS/inertial guidance system is guided toward the measured position, i.e., GPS coordinates of the SAM battery.
The location of the missile during flight is measured by the on-board GPS/inertial guidance system to facilitate missile guidance. However, GPS guidance systems are susceptible to jamming, such as via jamming transmitters located near the target. In addition, GPS/inertial guidance systems often employ an expensive five element null-steering antenna. The null-steering antenna is capable of steering nulls to four jamming units. Consequently, use of more than four jamming units can successfully jam the accompanying GPS/inertial guidance system by overcoming the weak GP signals from satellites.
An inertial measurement unit (IMU) is often coupled to the GPS receiver and is capable of continuing guidance after GPS jamming. However, IMU guidance becomes inaccurate if jamming occurs far from the target. Furthermore, errors introduced via the GPS/inertial guidance system augment initial target location measurement errors, reducing missile-targeting accuracy.
Radar, laser, sonar, and infrared target detecting and tracking systems are often employed to target and shoot moving targets. Such systems, which may be either passive or active systems, measure radar, optical, acoustical, or infrared energy emanating or reflecting from the target, respectively, to detect, track, and guide a missile toward the target. However, such systems often cannot accurately detect and target enemy miniature UAV's, which may be smaller than a model airplane.
Miniature UAV's are often quiet, electrically powered aircraft made of nonreflective (reflect little or no electromagnetic energy) materials. Accordingly, their radar, optical, acoustical, and infrared signatures are very small and difficult to detect using conventional methods. Furthermore, conventional radar, infrared, laser, and acoustical jamming and decoy systems may be employed to help UAV's evade detection.
Miniature UAV's are particularly dangerous, since television cameras or other communications equipment on UAV's may relay information about our troop positions and other reconnaissance to an enemy. UAV's may also be equipped with deadly ordinance.
Hence, a need exists in the art for an accurate target detecting, tracking and missile guidance system that is relatively immune to GPS, radar, laser, and infrared jamming and capable of detecting and destroying miniature UAV's.